1. Technical Field of the Invention
The present invention relates generally to mounting of heatsinks and the like to semiconductor devices, motherboards, and the like. More specifically, it relates to dampening measures for such mounting.
2. Background Art
FIG. 1 illustrates a known technique for mounting a heatsink 10 to a chip assembly on a motherboard 12. The chip assembly may, for example, include a microelectronic die 14 (such as a flip-chip die) connected by bumps 16 to a card 18 which is connected by solder balls 20 to the motherboard. Typically, thermal grease 22 is used to provide good thermal mating of the die and the heatsink.
In applications where the heatsink is quite heavy, springs 24 are used to support the weight of the heatsink, taking the weight off of the die and card. The heatsink is attached, and the springs are drawn into compression, by bolts 26 and nuts 28.
While the springs may do an adequate job of supporting the heatsink under stationary conditions, they have been found inadequate in applications where the assembly is subject to significant shock or vibration.
FIG. 2 illustrates one problem that exists in this prior art. When subjected to shock or vibration, the heatsink travels downward, further compressing the spring. If the shock or vibration is severe enough in amplitude or duration, the heatsink may eventually impact the die with sufficient force to break the die or at least some of the interconnects. In the prior art, the solution has been to use stiffer springs in such applications, to reduce the tendency of the heatsink to impact the die. Unfortunately, this introduces another problem.
FIG. 3 illustrates what can happen if the springs are too strong and/or are drawn down with excessive preload and/or if the heatsink is subjected to shock or vibration with a significant upward component. In severe cases, the motherboard itself may fracture or suffer failure of its electrical traces or other devices. Even if the springs are not the problem, the motherboard may fail on its own, due to vibration or oscillation.
It is desirable to dampen the movement of the heatsink and motherboard relative to each other and relative to the other components of the assembly.